Novel electrochemical/fluorescence dual-mode biosensor based on covalent organic framework for tetracycline detection

Excessive antibiotic residues increased the environmental damage and safety of animal products, leading to serious health threats. In this study, a dual-mode probe was developed and applied as an electrochemical/ fluorescence sensor for tetracycline (TET) detection. The probe, comprising a fluorescent covalent organic framework, electroactive methylene blue, gold nanoparticles (AuNPs) and single-stranded DNA, was synthesized by self-assembly. A glassy carbon electrode was functionalized with molybdenum disulfide nanosheets, AuNPs, and aptamers. The probe exhibited fluorescent signals in solution and electrochemical signals after being specifically connected to the electrode via hybridization. In the presence of TET, the probe is be competitively expelled from the modified electrode, resulting in an increase in the fluorescent signal and a decrease in the electrochemical signal. The developed electrochemical/fluorescence dual-mode sensor enabled sensitive TET detection in the concentration range of 10 nM-10 mM, with minimum detection limits of 0.03 nM (electrochemical) and 0.05 nM (fluorescence). With its high selectivity, superior reproducibility, and excellent stability, the proposed dual-mode sensor demonstrates high reliability, and excellent application prospects for TET detection in milk and river water samples.